1. Field of the Invention
This invention relates generally to railway rail-and-fastening assemblies and particularly to a device suitable for use in such an assembly to electrically insulate a rail from a rail clip, which bears downwardly upon the upper surface of the rail flange, and from an anchorage, beside the rail flange, for the rail clip.
2. DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 3,004,716 (Pande-Rolfsen) discloses a rail clip made by bending a metal bar of circular cross-section. U.S. Pat. No. 3,297,253 (Astley et al) discloses a railway rail-and-fastening assembly in which a substantially straight leg of substantially the same clip is driven into a horizontal passageway through an anchorage, beside the rail flange, which is formed by the upper portion of a cast metal anchoring member, this portion projecting out of a concrete rail tie and another portion being embedded in the tie. Another portion of the clip bears downwardly upon the upper surface of the rail flange and a further portion of the clip bears downwardly upon the anchoring member at a location which, as seen from the rail, is beyond the passageway. It is desired to use the rail to carry electric currents for signalling purposes and since the concrete tie, the clip and the anchoring member are all good conductors of electricity the rail is electrically insulated from all of them by interposing a rubber pad between the top of the tie and the bottom of the rail flange and by using a one-piece elongate nylon insulator of substantially L-shaped cross-section, one limb of which is inclined to the horizontal and is interposed between the upper surface of the rail flange and the portion of the clip which bears downwardly upon that surface, whilst the other limb is vertical and is interposed between the edge of the rail flange and the anchoring member. Two lugs extend, from opposite ends of the vertical limb of the insulator, away from the other limb and they project on opposite sides of the anchoring member to limit movement of the insulator along the rail. Most of these insulators made to date have had the first-mentioned limb, i.e. the inclined limb, no more than about 4 millimeters thick. There is a tendency for the clip to sink into the insulator after a while, thus changing the geometry of the clip, and therefore the load which it exerts on the rail, and in extreme cases this has led to piercing of the insulator so that the clip directly contacted the rail. Several solutions to this problem have been proposed including increasing from the beginning the area of contact between clip and insulator by having a flat surface on the clip where it contacts the insulator -- see U.S. Pat. No. 3,658,246 (Davies). Another solution was to make a composite device, for use in insulating a rail from a rail clip and from an anchorage for the clip, the device being in two parts, a metal part and a plastic part, each of substantially L-shaped cross-section and having an inclined limb and a vertical limb as described above, the clip bearing on the inclined limb of the metal part which bears on the inclined limb of the plastic part which bears on the upper surface of the rail flange -- see U.S. Pat. No. 3,463,394 (Jones et al) for example. All the United States patents mentioned above have been assigned to a company to which my present invention is also assigned, a company which was formerly called Lockspike Limited but is now called Pandrol Limited.
South African Patent Application 75/6770 in the name of an associated company, Pandrol (Proprietary) Limited, discloses making the inclined limb of the one-piece insulator thicker than previously and making the insulator of glass fibre-reinforced plastic material. British Patent Application No. 44949/76, claiming priority from the South African application and in the name of Pandrol Limited, specifies that the thickness of the electrically insulating material of the inclined limb of the one-piece insulator should be more than 5mm., better more than 6mm., better still more than 7mm. and even better more than 8mm. and specifies that the insulator should be of fibre-reinforced plastic material, the fibre preferably being glass fibre and the plastic material preferably being nylon. None of the above ideas was conceived by me. In addition to these ideas my invention is disclosed in British application 44949/76 but not in South African application No. 75/6770.